ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/IO-AIO/README

Comparing IO-AIO/README (file contents):
Revision 1.18 by root, Thu Oct 26 16:28:33 2006 UTC vs.
Revision 1.35 by root, Tue Apr 21 20:06:05 2009 UTC

…		…
3		3
4	SYNOPSIS	4	SYNOPSIS
5	use IO::AIO;	5	use IO::AIO;
6		6
7	aio_open "/etc/passwd", O_RDONLY, 0, sub {	7	aio_open "/etc/passwd", O_RDONLY, 0, sub {
8	my ($fh) = @_;	8	my $fh = shift
		9	or die "/etc/passwd: $!";
9	...	10	...
10	};	11	};
11		12
12	aio_unlink "/tmp/file", sub { };	13	aio_unlink "/tmp/file", sub { };
13		14
…		…
23	$req->cancel; # cancel request if still in queue	24	$req->cancel; # cancel request if still in queue
24		25
25	my $grp = aio_group sub { print "all stats done\n" };	26	my $grp = aio_group sub { print "all stats done\n" };
26	add $grp aio_stat "..." for ...;	27	add $grp aio_stat "..." for ...;
27		28
		29	# AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
		30	use AnyEvent::AIO;
		31
28	# AnyEvent integration	32	# EV integration
29	open my $fh, "<&=" . IO::AIO::poll_fileno or die "$!";	33	my $w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
30	my $w = AnyEvent->io (fh => $fh, poll => 'r', cb => sub { IO::AIO::poll_cb });
31		34
32	# Event integration	35	# Event integration
33	Event->io (fd => IO::AIO::poll_fileno,	36	Event->io (fd => IO::AIO::poll_fileno,
34	poll => 'r',	37	poll => 'r',
35	cb => \&IO::AIO::poll_cb);	38	cb => \&IO::AIO::poll_cb);
…		…
47	\&IO::AIO::poll_cb);	50	\&IO::AIO::poll_cb);
48		51
49	DESCRIPTION	52	DESCRIPTION
50	This module implements asynchronous I/O using whatever means your	53	This module implements asynchronous I/O using whatever means your
51	operating system supports.	54	operating system supports.
		55
		56	Asynchronous means that operations that can normally block your program
		57	(e.g. reading from disk) will be done asynchronously: the operation will
		58	still block, but you can do something else in the meantime. This is
		59	extremely useful for programs that need to stay interactive even when
		60	doing heavy I/O (GUI programs, high performance network servers etc.),
		61	but can also be used to easily do operations in parallel that are
		62	normally done sequentially, e.g. stat'ing many files, which is much
		63	faster on a RAID volume or over NFS when you do a number of stat
		64	operations concurrently.
		65
		66	While most of this works on all types of file descriptors (for example
		67	sockets), using these functions on file descriptors that support
		68	nonblocking operation (again, sockets, pipes etc.) is very inefficient.
		69	Use an event loop for that (such as the Event module): IO::AIO will
		70	naturally fit into such an event loop itself.
52		71
53	In this version, a number of threads are started that execute your	72	In this version, a number of threads are started that execute your
54	requests and signal their completion. You don't need thread support in	73	requests and signal their completion. You don't need thread support in
55	perl, and the threads created by this module will not be visible to	74	perl, and the threads created by this module will not be visible to
56	perl. In the future, this module might make use of the native aio	75	perl. In the future, this module might make use of the native aio
57	functions available on many operating systems. However, they are often	76	functions available on many operating systems. However, they are often
58	not well-supported or restricted (Linux doesn't allow them on normal	77	not well-supported or restricted (GNU/Linux doesn't allow them on normal
59	files currently, for example), and they would only support aio_read and	78	files currently, for example), and they would only support aio_read and
60	aio_write, so the remaining functionality would have to be implemented	79	aio_write, so the remaining functionality would have to be implemented
61	using threads anyway.	80	using threads anyway.
62		81
63	Although the module will work with in the presence of other (Perl-)	82	Although the module will work in the presence of other (Perl-) threads,
64	threads, it is currently not reentrant in any way, so use appropriate	83	it is currently not reentrant in any way, so use appropriate locking
65	locking yourself, always call "poll_cb" from within the same thread, or	84	yourself, always call "poll_cb" from within the same thread, or never
66	never call "poll_cb" (or other "aio_" functions) recursively.	85	call "poll_cb" (or other "aio_" functions) recursively.
		86
		87	EXAMPLE
		88	This is a simple example that uses the Event module and loads
		89	/etc/passwd asynchronously:
		90
		91	use Fcntl;
		92	use Event;
		93	use IO::AIO;
		94
		95	# register the IO::AIO callback with Event
		96	Event->io (fd => IO::AIO::poll_fileno,
		97	poll => 'r',
		98	cb => \&IO::AIO::poll_cb);
		99
		100	# queue the request to open /etc/passwd
		101	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		102	my $fh = shift
		103	or die "error while opening: $!";
		104
		105	# stat'ing filehandles is generally non-blocking
		106	my $size = -s $fh;
		107
		108	# queue a request to read the file
		109	my $contents;
		110	aio_read $fh, 0, $size, $contents, 0, sub {
		111	$_[0] == $size
		112	or die "short read: $!";
		113
		114	close $fh;
		115
		116	# file contents now in $contents
		117	print $contents;
		118
		119	# exit event loop and program
		120	Event::unloop;
		121	};
		122	};
		123
		124	# possibly queue up other requests, or open GUI windows,
		125	# check for sockets etc. etc.
		126
		127	# process events as long as there are some:
		128	Event::loop;
67		129
68	REQUEST ANATOMY AND LIFETIME	130	REQUEST ANATOMY AND LIFETIME
69	Every "aio_*" function creates a request. which is a C data structure	131	Every "aio_*" function creates a request. which is a C data structure
70	not directly visible to Perl.	132	not directly visible to Perl.
71		133
…		…
107	anymore (except possibly for the Perl object, but its connection to	169	anymore (except possibly for the Perl object, but its connection to
108	the actual aio request is severed and calling its methods will	170	the actual aio request is severed and calling its methods will
109	either do nothing or result in a runtime error).	171	either do nothing or result in a runtime error).
110		172
111	FUNCTIONS	173	FUNCTIONS
112	AIO FUNCTIONS	174	AIO REQUEST FUNCTIONS
113	All the "aio_*" calls are more or less thin wrappers around the	175	All the "aio_*" calls are more or less thin wrappers around the syscall
114	syscall with the same name (sans "aio_"). The arguments are similar	176	with the same name (sans "aio_"). The arguments are similar or
115	or identical, and they all accept an additional (and optional)	177	identical, and they all accept an additional (and optional) $callback
116	$callback argument which must be a code reference. This code	178	argument which must be a code reference. This code reference will get
117	reference will get called with the syscall return code (e.g. most	179	called with the syscall return code (e.g. most syscalls return -1 on
118	syscalls return -1 on error, unlike perl, which usually delivers	180	error, unlike perl, which usually delivers "false") as its sole argument
119	"false") as it's sole argument when the given syscall has been	181	after the given syscall has been executed asynchronously.
120	executed asynchronously.
121		182
122	All functions expecting a filehandle keep a copy of the filehandle	183	All functions expecting a filehandle keep a copy of the filehandle
123	internally until the request has finished.	184	internally until the request has finished.
124		185
125	All requests return objects of type IO::AIO::REQ that allow further	186	All functions return request objects of type IO::AIO::REQ that allow
126	manipulation of those requests while they are in-flight.	187	further manipulation of those requests while they are in-flight.
127		188
128	The pathnames you pass to these routines *must* be absolute and	189	The pathnames you pass to these routines *must* be absolute and encoded
129	encoded in byte form. The reason for the former is that at the time	190	as octets. The reason for the former is that at the time the request is
130	the request is being executed, the current working directory could	191	being executed, the current working directory could have changed.
131	have changed. Alternatively, you can make sure that you never change	192	Alternatively, you can make sure that you never change the current
132	the current working directory.	193	working directory anywhere in the program and then use relative paths.
133		194
134	To encode pathnames to byte form, either make sure you either: a)	195	To encode pathnames as octets, either make sure you either: a) always
135	always pass in filenames you got from outside (command line, readdir	196	pass in filenames you got from outside (command line, readdir etc.)
136	etc.), b) are ASCII or ISO 8859-1, c) use the Encode module and	197	without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
137	encode your pathnames to the locale (or other) encoding in effect in	198	and encode your pathnames to the locale (or other) encoding in effect in
138	the user environment, d) use Glib::filename_from_unicode on unicode	199	the user environment, d) use Glib::filename_from_unicode on unicode
139	filenames or e) use something else.	200	filenames or e) use something else to ensure your scalar has the correct
		201	contents.
140		202
		203	This works, btw. independent of the internal UTF-8 bit, which IO::AIO
		204	handles correctly whether it is set or not.
		205
141	$prev_pri = aioreq_pri [$pri]	206	$prev_pri = aioreq_pri [$pri]
142	Returns the priority value that would be used for the next	207	Returns the priority value that would be used for the next request
143	request and, if $pri is given, sets the priority for the next	208	and, if $pri is given, sets the priority for the next aio request.
144	aio request.
145		209
146	The default priority is 0, the minimum and maximum priorities	210	The default priority is 0, the minimum and maximum priorities are -4
147	are -4 and 4, respectively. Requests with higher priority will	211	and 4, respectively. Requests with higher priority will be serviced
148	be serviced first.	212	first.
149		213
150	The priority will be reset to 0 after each call to one of the	214	The priority will be reset to 0 after each call to one of the
151	"aio_*" functions.	215	"aio_*" functions.
152		216
153	Example: open a file with low priority, then read something from	217	Example: open a file with low priority, then read something from it
154	it with higher priority so the read request is serviced before	218	with higher priority so the read request is serviced before other
155	other low priority open requests (potentially spamming the	219	low priority open requests (potentially spamming the cache):
156	cache):
157		220
		221	aioreq_pri -3;
		222	aio_open ..., sub {
		223	return unless $_[0];
		224
158	aioreq_pri -3;	225	aioreq_pri -2;
159	aio_open ..., sub {
160	return unless $_[0];
161
162	aioreq_pri -2;
163	aio_read $_[0], ..., sub {	226	aio_read $_[0], ..., sub {
164	...
165	};
166	};
167
168	aioreq_nice $pri_adjust
169	Similar to "aioreq_pri", but subtracts the given value from the
170	current priority, so effects are cumulative.
171
172	aio_open $pathname, $flags, $mode, $callback->($fh)
173	Asynchronously open or create a file and call the callback with
174	a newly created filehandle for the file.
175
176	The pathname passed to "aio_open" must be absolute. See API
177	NOTES, above, for an explanation.
178
179	The $flags argument is a bitmask. See the "Fcntl" module for a
180	list. They are the same as used by "sysopen".
181
182	Likewise, $mode specifies the mode of the newly created file, if
183	it didn't exist and "O_CREAT" has been given, just like perl's
184	"sysopen", except that it is mandatory (i.e. use 0 if you don't
185	create new files, and 0666 or 0777 if you do).
186
187	Example:
188
189	aio_open "/etc/passwd", O_RDONLY, 0, sub {
190	if ($_[0]) {
191	print "open successful, fh is $_[0]\n";
192	...
193	} else {
194	die "open failed: $!\n";
195	}
196	};
197
198	aio_close $fh, $callback->($status)
199	Asynchronously close a file and call the callback with the
200	result code. *WARNING:* although accepted, you should not pass
201	in a perl filehandle here, as perl will likely close the file
202	descriptor another time when the filehandle is destroyed.
203	Normally, you can safely call perls "close" or just let
204	filehandles go out of scope.
205
206	This is supposed to be a bug in the API, so that might change.
207	It's therefore best to avoid this function.
208
209	aio_read $fh,$offset,$length, $data,$dataoffset,
210	$callback->($retval)
211	aio_write $fh,$offset,$length, $data,$dataoffset,
212	$callback->($retval)
213	Reads or writes "length" bytes from the specified "fh" and
214	"offset" into the scalar given by "data" and offset "dataoffset"
215	and calls the callback without the actual number of bytes read
216	(or -1 on error, just like the syscall).
217
218	The $data scalar *MUST NOT* be modified in any way while the
219	request is outstanding. Modifying it can result in segfaults or
220	WW3 (if the necessary/optional hardware is installed).
221
222	Example: Read 15 bytes at offset 7 into scalar $buffer, starting
223	at offset 0 within the scalar:
224
225	aio_read $fh, 7, 15, $buffer, 0, sub {
226	$_[0] > 0 or die "read error: $!";
227	print "read $_[0] bytes: <$buffer>\n";
228	};
229
230	aio_move $srcpath, $dstpath, $callback->($status)
231	Try to move the *file* (directories not supported as either
232	source or destination) from $srcpath to $dstpath and call the
233	callback with the 0 (error) or -1 ok.
234
235	This is a composite request that tries to rename(2) the file
236	first. If rename files with "EXDEV", it creates the destination
237	file with mode 0200 and copies the contents of the source file
238	into it using "aio_sendfile", followed by restoring atime,
239	mtime, access mode and uid/gid, in that order, and unlinking the
240	$srcpath.
241
242	If an error occurs, the partial destination file will be
243	unlinked, if possible, except when setting atime, mtime, access
244	mode and uid/gid, where errors are being ignored.
245
246	aio_sendfile $out_fh, $in_fh, $in_offset, $length,
247	$callback->($retval)
248	Tries to copy $length bytes from $in_fh to $out_fh. It starts
249	reading at byte offset $in_offset, and starts writing at the
250	current file offset of $out_fh. Because of that, it is not safe
251	to issue more than one "aio_sendfile" per $out_fh, as they will
252	interfere with each other.
253
254	This call tries to make use of a native "sendfile" syscall to
255	provide zero-copy operation. For this to work, $out_fh should
256	refer to a socket, and $in_fh should refer to mmap'able file.
257
258	If the native sendfile call fails or is not implemented, it will
259	be emulated, so you can call "aio_sendfile" on any type of
260	filehandle regardless of the limitations of the operating
261	system.
262
263	Please note, however, that "aio_sendfile" can read more bytes
264	from $in_fh than are written, and there is no way to find out
265	how many bytes have been read from "aio_sendfile" alone, as
266	"aio_sendfile" only provides the number of bytes written to
267	$out_fh. Only if the result value equals $length one can assume
268	that $length bytes have been read.
269
270	aio_readahead $fh,$offset,$length, $callback->($retval)
271	"aio_readahead" populates the page cache with data from a file
272	so that subsequent reads from that file will not block on disk
273	I/O. The $offset argument specifies the starting point from
274	which data is to be read and $length specifies the number of
275	bytes to be read. I/O is performed in whole pages, so that
276	offset is effectively rounded down to a page boundary and bytes
277	are read up to the next page boundary greater than or equal to
278	(off-set+length). "aio_readahead" does not read beyond the end
279	of the file. The current file offset of the file is left
280	unchanged.
281
282	If that syscall doesn't exist (likely if your OS isn't Linux) it
283	will be emulated by simply reading the data, which would have a
284	similar effect.
285
286	aio_stat $fh_or_path, $callback->($status)
287	aio_lstat $fh, $callback->($status)
288	Works like perl's "stat" or "lstat" in void context. The
289	callback will be called after the stat and the results will be
290	available using "stat _" or "-s _" etc...
291
292	The pathname passed to "aio_stat" must be absolute. See API
293	NOTES, above, for an explanation.
294
295	Currently, the stats are always 64-bit-stats, i.e. instead of
296	returning an error when stat'ing a large file, the results will
297	be silently truncated unless perl itself is compiled with large
298	file support.
299
300	Example: Print the length of /etc/passwd:
301
302	aio_stat "/etc/passwd", sub {
303	$_[0] and die "stat failed: $!";
304	print "size is ", -s _, "\n";
305	};
306
307	aio_unlink $pathname, $callback->($status)
308	Asynchronously unlink (delete) a file and call the callback with
309	the result code.
310
311	aio_link $srcpath, $dstpath, $callback->($status)
312	Asynchronously create a new link to the existing object at
313	$srcpath at the path $dstpath and call the callback with the
314	result code.
315
316	aio_symlink $srcpath, $dstpath, $callback->($status)
317	Asynchronously create a new symbolic link to the existing object
318	at $srcpath at the path $dstpath and call the callback with the
319	result code.
320
321	aio_rename $srcpath, $dstpath, $callback->($status)
322	Asynchronously rename the object at $srcpath to $dstpath, just
323	as rename(2) and call the callback with the result code.
324
325	aio_rmdir $pathname, $callback->($status)
326	Asynchronously rmdir (delete) a directory and call the callback
327	with the result code.
328
329	aio_readdir $pathname, $callback->($entries)
330	Unlike the POSIX call of the same name, "aio_readdir" reads an
331	entire directory (i.e. opendir + readdir + closedir). The
332	entries will not be sorted, and will NOT include the "." and
333	".." entries.
334
335	The callback a single argument which is either "undef" or an
336	array-ref with the filenames.
337
338	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
339	Scans a directory (similar to "aio_readdir") but additionally
340	tries to efficiently separate the entries of directory $path
341	into two sets of names, directories you can recurse into
342	(directories), and ones you cannot recurse into (everything
343	else, including symlinks to directories).
344
345	"aio_scandir" is a composite request that creates of many sub
346	requests_ $maxreq specifies the maximum number of outstanding
347	aio requests that this function generates. If it is "<= 0", then
348	a suitable default will be chosen (currently 6).
349
350	On error, the callback is called without arguments, otherwise it
351	receives two array-refs with path-relative entry names.
352
353	Example:
354
355	aio_scandir $dir, 0, sub {
356	my ($dirs, $nondirs) = @_;
357	print "real directories: @$dirs\n";
358	print "everything else: @$nondirs\n";
359	};
360
361	Implementation notes.
362
363	The "aio_readdir" cannot be avoided, but "stat()"'ing every
364	entry can.
365
366	After reading the directory, the modification time, size etc. of
367	the directory before and after the readdir is checked, and if
368	they match (and isn't the current time), the link count will be
369	used to decide how many entries are directories (if >= 2).
370	Otherwise, no knowledge of the number of subdirectories will be
371	assumed.
372
373	Then entries will be sorted into likely directories (everything
374	without a non-initial dot currently) and likely non-directories
375	(everything else). Then every entry plus an appended "/." will
376	be "stat"'ed, likely directories first. If that succeeds, it
377	assumes that the entry is a directory or a symlink to directory
378	(which will be checked seperately). This is often faster than
379	stat'ing the entry itself because filesystems might detect the
380	type of the entry without reading the inode data (e.g. ext2fs
381	filetype feature).
382
383	If the known number of directories (link count - 2) has been
384	reached, the rest of the entries is assumed to be
385	non-directories.
386
387	This only works with certainty on POSIX (= UNIX) filesystems,
388	which fortunately are the vast majority of filesystems around.
389
390	It will also likely work on non-POSIX filesystems with reduced
391	efficiency as those tend to return 0 or 1 as link counts, which
392	disables the directory counting heuristic.
393
394	aio_fsync $fh, $callback->($status)
395	Asynchronously call fsync on the given filehandle and call the
396	callback with the fsync result code.
397
398	aio_fdatasync $fh, $callback->($status)
399	Asynchronously call fdatasync on the given filehandle and call
400	the callback with the fdatasync result code.
401
402	If this call isn't available because your OS lacks it or it
403	couldn't be detected, it will be emulated by calling "fsync"
404	instead.
405
406	aio_group $callback->(...)
407	This is a very special aio request: Instead of doing something,
408	it is a container for other aio requests, which is useful if you
409	want to bundle many requests into a single, composite, request
410	with a definite callback and the ability to cancel the whole
411	request with its subrequests.
412
413	Returns an object of class IO::AIO::GRP. See its documentation
414	below for more info.
415
416	Example:
417
418	my $grp = aio_group sub {
419	print "all stats done\n";
420	};
421
422	add $grp
423	(aio_stat ...),
424	(aio_stat ...),
425	...;	227	...
426
427	aio_nop $callback->()
428	This is a special request - it does nothing in itself and is
429	only used for side effects, such as when you want to add a dummy
430	request to a group so that finishing the requests in the group
431	depends on executing the given code.
432
433	While this request does nothing, it still goes through the
434	execution phase and still requires a worker thread. Thus, the
435	callback will not be executed immediately but only after other
436	requests in the queue have entered their execution phase. This
437	can be used to measure request latency.
438
439	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
440	Mainly used for debugging and benchmarking, this aio request
441	puts one of the request workers to sleep for the given time.
442
443	While it is theoretically handy to have simple I/O scheduling
444	requests like sleep and file handle readable/writable, the
445	overhead this creates is immense (it blocks a thread for a long
446	time) so do not use this function except to put your application
447	under artificial I/O pressure.
448
449	IO::AIO::REQ CLASS
450	All non-aggregate "aio_*" functions return an object of this class
451	when called in non-void context.
452
453	cancel $req
454	Cancels the request, if possible. Has the effect of skipping
455	execution when entering the execute state and skipping calling
456	the callback when entering the the result state, but will leave
457	the request otherwise untouched. That means that requests that
458	currently execute will not be stopped and resources held by the
459	request will not be freed prematurely.
460
461	cb $req $callback->(...)
462	Replace (or simply set) the callback registered to the request.
463
464	IO::AIO::GRP CLASS
465	This class is a subclass of IO::AIO::REQ, so all its methods apply
466	to objects of this class, too.
467
468	A IO::AIO::GRP object is a special request that can contain multiple
469	other aio requests.
470
471	You create one by calling the "aio_group" constructing function with
472	a callback that will be called when all contained requests have
473	entered the "done" state:
474
475	my $grp = aio_group sub {
476	print "all requests are done\n";
477	};
478
479	You add requests by calling the "add" method with one or more
480	"IO::AIO::REQ" objects:
481
482	$grp->add (aio_unlink "...");
483
484	add $grp aio_stat "...", sub {
485	$_[0] or return $grp->result ("error");
486
487	# add another request dynamically, if first succeeded
488	add $grp aio_open "...", sub {
489	$grp->result ("ok");
490	};	228	};
491	};	229	};
492		230
		231	aioreq_nice $pri_adjust
		232	Similar to "aioreq_pri", but subtracts the given value from the
		233	current priority, so the effect is cumulative.
		234
		235	aio_open $pathname, $flags, $mode, $callback->($fh)
		236	Asynchronously open or create a file and call the callback with a
		237	newly created filehandle for the file.
		238
		239	The pathname passed to "aio_open" must be absolute. See API NOTES,
		240	above, for an explanation.
		241
		242	The $flags argument is a bitmask. See the "Fcntl" module for a list.
		243	They are the same as used by "sysopen".
		244
		245	Likewise, $mode specifies the mode of the newly created file, if it
		246	didn't exist and "O_CREAT" has been given, just like perl's
		247	"sysopen", except that it is mandatory (i.e. use 0 if you don't
		248	create new files, and 0666 or 0777 if you do). Note that the $mode
		249	will be modified by the umask in effect then the request is being
		250	executed, so better never change the umask.
		251
		252	Example:
		253
		254	aio_open "/etc/passwd", O_RDONLY, 0, sub {
		255	if ($_[0]) {
		256	print "open successful, fh is $_[0]\n";
		257	...
		258	} else {
		259	die "open failed: $!\n";
		260	}
		261	};
		262
		263	aio_close $fh, $callback->($status)
		264	Asynchronously close a file and call the callback with the result
		265	code.
		266
		267	Unfortunately, you can't do this to perl. Perl *insists* very
		268	strongly on closing the file descriptor associated with the
		269	filehandle itself.
		270
		271	Therefore, "aio_close" will not close the filehandle - instead it
		272	will use dup2 to overwrite the file descriptor with the write-end of
		273	a pipe (the pipe fd will be created on demand and will be cached).
		274
		275	Or in other words: the file descriptor will be closed, but it will
		276	not be free for reuse until the perl filehandle is closed.
		277
		278	aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		279	aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
		280	Reads or writes $length bytes from or to the specified $fh and
		281	$offset into the scalar given by $data and offset $dataoffset and
		282	calls the callback without the actual number of bytes read (or -1 on
		283	error, just like the syscall).
		284
		285	"aio_read" will, like "sysread", shrink or grow the $data scalar to
		286	offset plus the actual number of bytes read.
		287
		288	If $offset is undefined, then the current file descriptor offset
		289	will be used (and updated), otherwise the file descriptor offset
		290	will not be changed by these calls.
		291
		292	If $length is undefined in "aio_write", use the remaining length of
		293	$data.
		294
		295	If $dataoffset is less than zero, it will be counted from the end of
		296	$data.
		297
		298	The $data scalar *MUST NOT* be modified in any way while the request
		299	is outstanding. Modifying it can result in segfaults or World War
		300	III (if the necessary/optional hardware is installed).
		301
		302	Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
		303	offset 0 within the scalar:
		304
		305	aio_read $fh, 7, 15, $buffer, 0, sub {
		306	$_[0] > 0 or die "read error: $!";
		307	print "read $_[0] bytes: <$buffer>\n";
		308	};
		309
		310	aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
		311	Tries to copy $length bytes from $in_fh to $out_fh. It starts
		312	reading at byte offset $in_offset, and starts writing at the current
		313	file offset of $out_fh. Because of that, it is not safe to issue
		314	more than one "aio_sendfile" per $out_fh, as they will interfere
		315	with each other.
		316
		317	This call tries to make use of a native "sendfile" syscall to
		318	provide zero-copy operation. For this to work, $out_fh should refer
		319	to a socket, and $in_fh should refer to mmap'able file.
		320
		321	If the native sendfile call fails or is not implemented, it will be
		322	emulated, so you can call "aio_sendfile" on any type of filehandle
		323	regardless of the limitations of the operating system.
		324
		325	Please note, however, that "aio_sendfile" can read more bytes from
		326	$in_fh than are written, and there is no way to find out how many
		327	bytes have been read from "aio_sendfile" alone, as "aio_sendfile"
		328	only provides the number of bytes written to $out_fh. Only if the
		329	result value equals $length one can assume that $length bytes have
		330	been read.
		331
		332	aio_readahead $fh,$offset,$length, $callback->($retval)
		333	"aio_readahead" populates the page cache with data from a file so
		334	that subsequent reads from that file will not block on disk I/O. The
		335	$offset argument specifies the starting point from which data is to
		336	be read and $length specifies the number of bytes to be read. I/O is
		337	performed in whole pages, so that offset is effectively rounded down
		338	to a page boundary and bytes are read up to the next page boundary
		339	greater than or equal to (off-set+length). "aio_readahead" does not
		340	read beyond the end of the file. The current file offset of the file
		341	is left unchanged.
		342
		343	If that syscall doesn't exist (likely if your OS isn't Linux) it
		344	will be emulated by simply reading the data, which would have a
		345	similar effect.
		346
		347	aio_stat $fh_or_path, $callback->($status)
		348	aio_lstat $fh, $callback->($status)
		349	Works like perl's "stat" or "lstat" in void context. The callback
		350	will be called after the stat and the results will be available
		351	using "stat _" or "-s _" etc...
		352
		353	The pathname passed to "aio_stat" must be absolute. See API NOTES,
		354	above, for an explanation.
		355
		356	Currently, the stats are always 64-bit-stats, i.e. instead of
		357	returning an error when stat'ing a large file, the results will be
		358	silently truncated unless perl itself is compiled with large file
		359	support.
		360
		361	Example: Print the length of /etc/passwd:
		362
		363	aio_stat "/etc/passwd", sub {
		364	$_[0] and die "stat failed: $!";
		365	print "size is ", -s _, "\n";
		366	};
		367
		368	aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
		369	Works like perl's "utime" function (including the special case of
		370	$atime and $mtime being undef). Fractional times are supported if
		371	the underlying syscalls support them.
		372
		373	When called with a pathname, uses utimes(2) if available, otherwise
		374	utime(2). If called on a file descriptor, uses futimes(2) if
		375	available, otherwise returns ENOSYS, so this is not portable.
		376
		377	Examples:
		378
		379	# set atime and mtime to current time (basically touch(1)):
		380	aio_utime "path", undef, undef;
		381	# set atime to current time and mtime to beginning of the epoch:
		382	aio_utime "path", time, undef; # undef==0
		383
		384	aio_chown $fh_or_path, $uid, $gid, $callback->($status)
		385	Works like perl's "chown" function, except that "undef" for either
		386	$uid or $gid is being interpreted as "do not change" (but -1 can
		387	also be used).
		388
		389	Examples:
		390
		391	# same as "chown root path" in the shell:
		392	aio_chown "path", 0, -1;
		393	# same as above:
		394	aio_chown "path", 0, undef;
		395
		396	aio_truncate $fh_or_path, $offset, $callback->($status)
		397	Works like truncate(2) or ftruncate(2).
		398
		399	aio_chmod $fh_or_path, $mode, $callback->($status)
		400	Works like perl's "chmod" function.
		401
		402	aio_unlink $pathname, $callback->($status)
		403	Asynchronously unlink (delete) a file and call the callback with the
		404	result code.
		405
		406	aio_mknod $path, $mode, $dev, $callback->($status)
		407	[EXPERIMENTAL]
		408
		409	Asynchronously create a device node (or fifo). See mknod(2).
		410
		411	The only (POSIX-) portable way of calling this function is:
		412
		413	aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...
		414
		415	aio_link $srcpath, $dstpath, $callback->($status)
		416	Asynchronously create a new link to the existing object at $srcpath
		417	at the path $dstpath and call the callback with the result code.
		418
		419	aio_symlink $srcpath, $dstpath, $callback->($status)
		420	Asynchronously create a new symbolic link to the existing object at
		421	$srcpath at the path $dstpath and call the callback with the result
		422	code.
		423
		424	aio_readlink $path, $callback->($link)
		425	Asynchronously read the symlink specified by $path and pass it to
		426	the callback. If an error occurs, nothing or undef gets passed to
		427	the callback.
		428
		429	aio_rename $srcpath, $dstpath, $callback->($status)
		430	Asynchronously rename the object at $srcpath to $dstpath, just as
		431	rename(2) and call the callback with the result code.
		432
		433	aio_mkdir $pathname, $mode, $callback->($status)
		434	Asynchronously mkdir (create) a directory and call the callback with
		435	the result code. $mode will be modified by the umask at the time the
		436	request is executed, so do not change your umask.
		437
		438	aio_rmdir $pathname, $callback->($status)
		439	Asynchronously rmdir (delete) a directory and call the callback with
		440	the result code.
		441
		442	aio_readdir $pathname, $callback->($entries)
		443	Unlike the POSIX call of the same name, "aio_readdir" reads an
		444	entire directory (i.e. opendir + readdir + closedir). The entries
		445	will not be sorted, and will NOT include the "." and ".." entries.
		446
		447	The callback a single argument which is either "undef" or an
		448	array-ref with the filenames.
		449
		450	aio_load $path, $data, $callback->($status)
		451	This is a composite request that tries to fully load the given file
		452	into memory. Status is the same as with aio_read.
		453
		454	aio_copy $srcpath, $dstpath, $callback->($status)
		455	Try to copy the *file* (directories not supported as either source
		456	or destination) from $srcpath to $dstpath and call the callback with
		457	the 0 (error) or -1 ok.
		458
		459	This is a composite request that creates the destination file with
		460	mode 0200 and copies the contents of the source file into it using
		461	"aio_sendfile", followed by restoring atime, mtime, access mode and
		462	uid/gid, in that order.
		463
		464	If an error occurs, the partial destination file will be unlinked,
		465	if possible, except when setting atime, mtime, access mode and
		466	uid/gid, where errors are being ignored.
		467
		468	aio_move $srcpath, $dstpath, $callback->($status)
		469	Try to move the *file* (directories not supported as either source
		470	or destination) from $srcpath to $dstpath and call the callback with
		471	the 0 (error) or -1 ok.
		472
		473	This is a composite request that tries to rename(2) the file first;
		474	if rename fails with "EXDEV", it copies the file with "aio_copy"
		475	and, if that is successful, unlinks the $srcpath.
		476
		477	aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
		478	Scans a directory (similar to "aio_readdir") but additionally tries
		479	to efficiently separate the entries of directory $path into two sets
		480	of names, directories you can recurse into (directories), and ones
		481	you cannot recurse into (everything else, including symlinks to
		482	directories).
		483
		484	"aio_scandir" is a composite request that creates of many sub
		485	requests_ $maxreq specifies the maximum number of outstanding aio
		486	requests that this function generates. If it is "<= 0", then a
		487	suitable default will be chosen (currently 4).
		488
		489	On error, the callback is called without arguments, otherwise it
		490	receives two array-refs with path-relative entry names.
		491
		492	Example:
		493
		494	aio_scandir $dir, 0, sub {
		495	my ($dirs, $nondirs) = @_;
		496	print "real directories: @$dirs\n";
		497	print "everything else: @$nondirs\n";
		498	};
		499
		500	Implementation notes.
		501
		502	The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
		503	can.
		504
		505	After reading the directory, the modification time, size etc. of the
		506	directory before and after the readdir is checked, and if they match
		507	(and isn't the current time), the link count will be used to decide
		508	how many entries are directories (if >= 2). Otherwise, no knowledge
		509	of the number of subdirectories will be assumed.
		510
		511	Then entries will be sorted into likely directories (everything
		512	without a non-initial dot currently) and likely non-directories
		513	(everything else). Then every entry plus an appended "/." will be
		514	"stat"'ed, likely directories first. If that succeeds, it assumes
		515	that the entry is a directory or a symlink to directory (which will
		516	be checked seperately). This is often faster than stat'ing the entry
		517	itself because filesystems might detect the type of the entry
		518	without reading the inode data (e.g. ext2fs filetype feature).
		519
		520	If the known number of directories (link count - 2) has been
		521	reached, the rest of the entries is assumed to be non-directories.
		522
		523	This only works with certainty on POSIX (= UNIX) filesystems, which
		524	fortunately are the vast majority of filesystems around.
		525
		526	It will also likely work on non-POSIX filesystems with reduced
		527	efficiency as those tend to return 0 or 1 as link counts, which
		528	disables the directory counting heuristic.
		529
		530	aio_rmtree $path, $callback->($status)
		531	Delete a directory tree starting (and including) $path, return the
		532	status of the final "rmdir" only. This is a composite request that
		533	uses "aio_scandir" to recurse into and rmdir directories, and unlink
		534	everything else.
		535
		536	aio_sync $callback->($status)
		537	Asynchronously call sync and call the callback when finished.
		538
		539	aio_fsync $fh, $callback->($status)
		540	Asynchronously call fsync on the given filehandle and call the
		541	callback with the fsync result code.
		542
		543	aio_fdatasync $fh, $callback->($status)
		544	Asynchronously call fdatasync on the given filehandle and call the
		545	callback with the fdatasync result code.
		546
		547	If this call isn't available because your OS lacks it or it couldn't
		548	be detected, it will be emulated by calling "fsync" instead.
		549
		550	aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
		551	Sync the data portion of the file specified by $offset and $length
		552	to disk (but NOT the metadata), by calling the Linux-specific
		553	sync_file_range call. If sync_file_range is not available or it
		554	returns ENOSYS, then fdatasync or fsync is being substituted.
		555
		556	$flags can be a combination of
		557	"IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE",
		558	"IO::AIO::SYNC_FILE_RANGE_WRITE" and
		559	"IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER": refer to the sync_file_range
		560	manpage for details.
		561
		562	aio_pathsync $path, $callback->($status)
		563	This request tries to open, fsync and close the given path. This is
		564	a composite request intended to sync directories after directory
		565	operations (E.g. rename). This might not work on all operating
		566	systems or have any specific effect, but usually it makes sure that
		567	directory changes get written to disc. It works for anything that
		568	can be opened for read-only, not just directories.
		569
		570	Passes 0 when everything went ok, and -1 on error.
		571
		572	aio_group $callback->(...)
		573	This is a very special aio request: Instead of doing something, it
		574	is a container for other aio requests, which is useful if you want
		575	to bundle many requests into a single, composite, request with a
		576	definite callback and the ability to cancel the whole request with
		577	its subrequests.
		578
		579	Returns an object of class IO::AIO::GRP. See its documentation below
		580	for more info.
		581
		582	Example:
		583
		584	my $grp = aio_group sub {
		585	print "all stats done\n";
		586	};
		587
		588	add $grp
		589	(aio_stat ...),
		590	(aio_stat ...),
		591	...;
		592
		593	aio_nop $callback->()
		594	This is a special request - it does nothing in itself and is only
		595	used for side effects, such as when you want to add a dummy request
		596	to a group so that finishing the requests in the group depends on
		597	executing the given code.
		598
		599	While this request does nothing, it still goes through the execution
		600	phase and still requires a worker thread. Thus, the callback will
		601	not be executed immediately but only after other requests in the
		602	queue have entered their execution phase. This can be used to
		603	measure request latency.
		604
		605	IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
		606	Mainly used for debugging and benchmarking, this aio request puts
		607	one of the request workers to sleep for the given time.
		608
		609	While it is theoretically handy to have simple I/O scheduling
		610	requests like sleep and file handle readable/writable, the overhead
		611	this creates is immense (it blocks a thread for a long time) so do
		612	not use this function except to put your application under
		613	artificial I/O pressure.
		614
		615	IO::AIO::REQ CLASS
		616	All non-aggregate "aio_*" functions return an object of this class when
		617	called in non-void context.
		618
		619	cancel $req
		620	Cancels the request, if possible. Has the effect of skipping
		621	execution when entering the execute state and skipping calling the
		622	callback when entering the the result state, but will leave the
		623	request otherwise untouched. That means that requests that currently
		624	execute will not be stopped and resources held by the request will
		625	not be freed prematurely.
		626
		627	cb $req $callback->(...)
		628	Replace (or simply set) the callback registered to the request.
		629
		630	IO::AIO::GRP CLASS
		631	This class is a subclass of IO::AIO::REQ, so all its methods apply to
		632	objects of this class, too.
		633
		634	A IO::AIO::GRP object is a special request that can contain multiple
		635	other aio requests.
		636
		637	You create one by calling the "aio_group" constructing function with a
		638	callback that will be called when all contained requests have entered
		639	the "done" state:
		640
		641	my $grp = aio_group sub {
		642	print "all requests are done\n";
		643	};
		644
		645	You add requests by calling the "add" method with one or more
		646	"IO::AIO::REQ" objects:
		647
		648	$grp->add (aio_unlink "...");
		649
		650	add $grp aio_stat "...", sub {
		651	$_[0] or return $grp->result ("error");
		652
		653	# add another request dynamically, if first succeeded
		654	add $grp aio_open "...", sub {
		655	$grp->result ("ok");
		656	};
		657	};
		658
493	This makes it very easy to create composite requests (see the source	659	This makes it very easy to create composite requests (see the source of
494	of "aio_move" for an application) that work and feel like simple	660	"aio_move" for an application) that work and feel like simple requests.
		661
		662	* The IO::AIO::GRP objects will be cleaned up during calls to
		663	"IO::AIO::poll_cb", just like any other request.
		664
		665	* They can be canceled like any other request. Canceling will cancel
		666	not only the request itself, but also all requests it contains.
		667
		668	* They can also can also be added to other IO::AIO::GRP objects.
		669
		670	* You must not add requests to a group from within the group callback
		671	(or any later time).
		672
		673	Their lifetime, simplified, looks like this: when they are empty, they
		674	will finish very quickly. If they contain only requests that are in the
		675	"done" state, they will also finish. Otherwise they will continue to
		676	exist.
		677
		678	That means after creating a group you have some time to add requests
		679	(precisely before the callback has been invoked, which is only done
		680	within the "poll_cb"). And in the callbacks of those requests, you can
		681	add further requests to the group. And only when all those requests have
		682	finished will the the group itself finish.
		683
		684	add $grp ...
		685	$grp->add (...)
		686	Add one or more requests to the group. Any type of IO::AIO::REQ can
		687	be added, including other groups, as long as you do not create
		688	circular dependencies.
		689
		690	Returns all its arguments.
		691
		692	$grp->cancel_subs
		693	Cancel all subrequests and clears any feeder, but not the group
		694	request itself. Useful when you queued a lot of events but got a
		695	result early.
		696
		697	$grp->result (...)
		698	Set the result value(s) that will be passed to the group callback
		699	when all subrequests have finished and set the groups errno to the
		700	current value of errno (just like calling "errno" without an error
		701	number). By default, no argument will be passed and errno is zero.
		702
		703	$grp->errno ([$errno])
		704	Sets the group errno value to $errno, or the current value of errno
		705	when the argument is missing.
		706
		707	Every aio request has an associated errno value that is restored
		708	when the callback is invoked. This method lets you change this value
		709	from its default (0).
		710
		711	Calling "result" will also set errno, so make sure you either set $!
		712	before the call to "result", or call c<errno> after it.
		713
		714	feed $grp $callback->($grp)
		715	Sets a feeder/generator on this group: every group can have an
		716	attached generator that generates requests if idle. The idea behind
		717	this is that, although you could just queue as many requests as you
		718	want in a group, this might starve other requests for a potentially
		719	long time. For example, "aio_scandir" might generate hundreds of
		720	thousands "aio_stat" requests, delaying any later requests for a
		721	long time.
		722
		723	To avoid this, and allow incremental generation of requests, you can
		724	instead a group and set a feeder on it that generates those
		725	requests. The feed callback will be called whenever there are few
		726	enough (see "limit", below) requests active in the group itself and
		727	is expected to queue more requests.
		728
		729	The feed callback can queue as many requests as it likes (i.e. "add"
		730	does not impose any limits).
		731
		732	If the feed does not queue more requests when called, it will be
		733	automatically removed from the group.
		734
		735	If the feed limit is 0 when this method is called, it will be set to
		736	2 automatically.
		737
		738	Example:
		739
		740	# stat all files in @files, but only ever use four aio requests concurrently:
		741
		742	my $grp = aio_group sub { print "finished\n" };
		743	limit $grp 4;
		744	feed $grp sub {
		745	my $file = pop @files
		746	or return;
		747
		748	add $grp aio_stat $file, sub { ... };
		749	};
		750
		751	limit $grp $num
		752	Sets the feeder limit for the group: The feeder will be called
		753	whenever the group contains less than this many requests.
		754
		755	Setting the limit to 0 will pause the feeding process.
		756
		757	The default value for the limit is 0, but note that setting a feeder
		758	automatically bumps it up to 2.
		759
		760	SUPPORT FUNCTIONS
		761	EVENT PROCESSING AND EVENT LOOP INTEGRATION
		762	$fileno = IO::AIO::poll_fileno
		763	Return the *request result pipe file descriptor*. This filehandle
		764	must be polled for reading by some mechanism outside this module
		765	(e.g. Event or select, see below or the SYNOPSIS). If the pipe
		766	becomes readable you have to call "poll_cb" to check the results.
		767
		768	See "poll_cb" for an example.
		769
		770	IO::AIO::poll_cb
		771	Process some outstanding events on the result pipe. You have to call
		772	this regularly. Returns 0 if all events could be processed, or -1 if
		773	it returned earlier for whatever reason. Returns immediately when no
		774	events are outstanding. The amount of events processed depends on
		775	the settings of "IO::AIO::max_poll_req" and
		776	"IO::AIO::max_poll_time".
		777
		778	If not all requests were processed for whatever reason, the
		779	filehandle will still be ready when "poll_cb" returns, so normally
		780	you don't have to do anything special to have it called later.
		781
		782	Example: Install an Event watcher that automatically calls
		783	IO::AIO::poll_cb with high priority:
		784
		785	Event->io (fd => IO::AIO::poll_fileno,
		786	poll => 'r', async => 1,
		787	cb => \&IO::AIO::poll_cb);
		788
		789	IO::AIO::max_poll_reqs $nreqs
		790	IO::AIO::max_poll_time $seconds
		791	These set the maximum number of requests (default 0, meaning
		792	infinity) that are being processed by "IO::AIO::poll_cb" in one
		793	call, respectively the maximum amount of time (default 0, meaning
		794	infinity) spent in "IO::AIO::poll_cb" to process requests (more
		795	correctly the mininum amount of time "poll_cb" is allowed to use).
		796
		797	Setting "max_poll_time" to a non-zero value creates an overhead of
		798	one syscall per request processed, which is not normally a problem
		799	unless your callbacks are really really fast or your OS is really
		800	really slow (I am not mentioning Solaris here). Using
		801	"max_poll_reqs" incurs no overhead.
		802
		803	Setting these is useful if you want to ensure some level of
		804	interactiveness when perl is not fast enough to process all requests
		805	in time.
		806
		807	For interactive programs, values such as 0.01 to 0.1 should be fine.
		808
		809	Example: Install an Event watcher that automatically calls
		810	IO::AIO::poll_cb with low priority, to ensure that other parts of
		811	the program get the CPU sometimes even under high AIO load.
		812
		813	# try not to spend much more than 0.1s in poll_cb
		814	IO::AIO::max_poll_time 0.1;
		815
		816	# use a low priority so other tasks have priority
		817	Event->io (fd => IO::AIO::poll_fileno,
		818	poll => 'r', nice => 1,
		819	cb => &IO::AIO::poll_cb);
		820
		821	IO::AIO::poll_wait
		822	If there are any outstanding requests and none of them in the result
		823	phase, wait till the result filehandle becomes ready for reading
		824	(simply does a "select" on the filehandle. This is useful if you
		825	want to synchronously wait for some requests to finish).
		826
		827	See "nreqs" for an example.
		828
		829	IO::AIO::poll
		830	Waits until some requests have been handled.
		831
		832	Returns the number of requests processed, but is otherwise strictly
		833	equivalent to:
		834
		835	IO::AIO::poll_wait, IO::AIO::poll_cb
		836
		837	IO::AIO::flush
		838	Wait till all outstanding AIO requests have been handled.
		839
		840	Strictly equivalent to:
		841
		842	IO::AIO::poll_wait, IO::AIO::poll_cb
		843	while IO::AIO::nreqs;
		844
		845	CONTROLLING THE NUMBER OF THREADS
		846	IO::AIO::min_parallel $nthreads
		847	Set the minimum number of AIO threads to $nthreads. The current
		848	default is 8, which means eight asynchronous operations can execute
		849	concurrently at any one time (the number of outstanding requests,
		850	however, is unlimited).
		851
		852	IO::AIO starts threads only on demand, when an AIO request is queued
		853	and no free thread exists. Please note that queueing up a hundred
		854	requests can create demand for a hundred threads, even if it turns
		855	out that everything is in the cache and could have been processed
		856	faster by a single thread.
		857
		858	It is recommended to keep the number of threads relatively low, as
		859	some Linux kernel versions will scale negatively with the number of
		860	threads (higher parallelity => MUCH higher latency). With current
		861	Linux 2.6 versions, 4-32 threads should be fine.
		862
		863	Under most circumstances you don't need to call this function, as
		864	the module selects a default that is suitable for low to moderate
		865	load.
		866
		867	IO::AIO::max_parallel $nthreads
		868	Sets the maximum number of AIO threads to $nthreads. If more than
		869	the specified number of threads are currently running, this function
		870	kills them. This function blocks until the limit is reached.
		871
		872	While $nthreads are zero, aio requests get queued but not executed
		873	until the number of threads has been increased again.
		874
		875	This module automatically runs "max_parallel 0" at program end, to
		876	ensure that all threads are killed and that there are no outstanding
495	requests.	877	requests.
496		878
497	* The IO::AIO::GRP objects will be cleaned up during calls to
498	"IO::AIO::poll_cb", just like any other request.
499	* They can be canceled like any other request. Canceling will cancel
500	not only the request itself, but also all requests it contains.
501	* They can also can also be added to other IO::AIO::GRP objects.
502	* You must not add requests to a group from within the group
503	callback (or any later time).
504
505	Their lifetime, simplified, looks like this: when they are empty,
506	they will finish very quickly. If they contain only requests that
507	are in the "done" state, they will also finish. Otherwise they will
508	continue to exist.
509
510	That means after creating a group you have some time to add
511	requests. And in the callbacks of those requests, you can add
512	further requests to the group. And only when all those requests have
513	finished will the the group itself finish.
514
515	add $grp ...
516	$grp->add (...)
517	Add one or more requests to the group. Any type of IO::AIO::REQ
518	can be added, including other groups, as long as you do not
519	create circular dependencies.
520
521	Returns all its arguments.
522
523	$grp->cancel_subs
524	Cancel all subrequests and clears any feeder, but not the group
525	request itself. Useful when you queued a lot of events but got a
526	result early.
527
528	$grp->result (...)
529	Set the result value(s) that will be passed to the group
530	callback when all subrequests have finished and set thre groups
531	errno to the current value of errno (just like calling "errno"
532	without an error number). By default, no argument will be passed
533	and errno is zero.
534
535	$grp->errno ([$errno])
536	Sets the group errno value to $errno, or the current value of
537	errno when the argument is missing.
538
539	Every aio request has an associated errno value that is restored
540	when the callback is invoked. This method lets you change this
541	value from its default (0).
542
543	Calling "result" will also set errno, so make sure you either
544	set $! before the call to "result", or call c<errno> after it.
545
546	feed $grp $callback->($grp)
547	Sets a feeder/generator on this group: every group can have an
548	attached generator that generates requests if idle. The idea
549	behind this is that, although you could just queue as many
550	requests as you want in a group, this might starve other
551	requests for a potentially long time. For example, "aio_scandir"
552	might generate hundreds of thousands "aio_stat" requests,
553	delaying any later requests for a long time.
554
555	To avoid this, and allow incremental generation of requests, you
556	can instead a group and set a feeder on it that generates those
557	requests. The feed callback will be called whenever there are
558	few enough (see "limit", below) requests active in the group
559	itself and is expected to queue more requests.
560
561	The feed callback can queue as many requests as it likes (i.e.
562	"add" does not impose any limits).
563
564	If the feed does not queue more requests when called, it will be
565	automatically removed from the group.
566
567	If the feed limit is 0, it will be set to 2 automatically.
568
569	Example:
570
571	# stat all files in @files, but only ever use four aio requests concurrently:
572
573	my $grp = aio_group sub { print "finished\n" };
574	limit $grp 4;
575	feed $grp sub {
576	my $file = pop @files
577	or return;
578
579	add $grp aio_stat $file, sub { ... };
580	};
581
582	limit $grp $num
583	Sets the feeder limit for the group: The feeder will be called
584	whenever the group contains less than this many requests.
585
586	Setting the limit to 0 will pause the feeding process.
587
588	SUPPORT FUNCTIONS
589	$fileno = IO::AIO::poll_fileno
590	Return the *request result pipe file descriptor*. This
591	filehandle must be polled for reading by some mechanism outside
592	this module (e.g. Event or select, see below or the SYNOPSIS).
593	If the pipe becomes readable you have to call "poll_cb" to check
594	the results.
595
596	See "poll_cb" for an example.
597
598	IO::AIO::poll_cb
599	Process all outstanding events on the result pipe. You have to
600	call this regularly. Returns the number of events processed.
601	Returns immediately when no events are outstanding.
602
603	If not all requests were processed for whatever reason, the
604	filehandle will still be ready when "poll_cb" returns.
605
606	Example: Install an Event watcher that automatically calls
607	IO::AIO::poll_cb with high priority:
608
609	Event->io (fd => IO::AIO::poll_fileno,
610	poll => 'r', async => 1,
611	cb => \&IO::AIO::poll_cb);
612
613	IO::AIO::poll_some $max_requests
614	Similar to "poll_cb", but only processes up to $max_requests
615	requests at a time.
616
617	Useful if you want to ensure some level of interactiveness when
618	perl is not fast enough to process all requests in time.
619
620	Example: Install an Event watcher that automatically calls
621	IO::AIO::poll_some with low priority, to ensure that other parts
622	of the program get the CPU sometimes even under high AIO load.
623
624	Event->io (fd => IO::AIO::poll_fileno,
625	poll => 'r', nice => 1,
626	cb => sub { IO::AIO::poll_some 256 });
627
628	IO::AIO::poll_wait
629	Wait till the result filehandle becomes ready for reading
630	(simply does a "select" on the filehandle. This is useful if you
631	want to synchronously wait for some requests to finish).
632
633	See "nreqs" for an example.
634
635	IO::AIO::nreqs
636	Returns the number of requests currently in the ready, execute
637	or pending states (i.e. for which their callback has not been
638	invoked yet).
639
640	Example: wait till there are no outstanding requests anymore:
641
642	IO::AIO::poll_wait, IO::AIO::poll_cb
643	while IO::AIO::nreqs;
644
645	IO::AIO::nready
646	Returns the number of requests currently in the ready state (not
647	yet executed).
648
649	IO::AIO::npending
650	Returns the number of requests currently in the pending state
651	(executed, but not yet processed by poll_cb).
652
653	IO::AIO::flush
654	Wait till all outstanding AIO requests have been handled.
655
656	Strictly equivalent to:
657
658	IO::AIO::poll_wait, IO::AIO::poll_cb
659	while IO::AIO::nreqs;
660
661	IO::AIO::poll
662	Waits until some requests have been handled.
663
664	Strictly equivalent to:
665
666	IO::AIO::poll_wait, IO::AIO::poll_cb
667	if IO::AIO::nreqs;
668
669	IO::AIO::min_parallel $nthreads
670	Set the minimum number of AIO threads to $nthreads. The current
671	default is 8, which means eight asynchronous operations can
672	execute concurrently at any one time (the number of outstanding
673	requests, however, is unlimited).
674
675	IO::AIO starts threads only on demand, when an AIO request is
676	queued and no free thread exists.
677
678	It is recommended to keep the number of threads relatively low,
679	as some Linux kernel versions will scale negatively with the
680	number of threads (higher parallelity => MUCH higher latency).
681	With current Linux 2.6 versions, 4-32 threads should be fine.
682
683	Under most circumstances you don't need to call this function,
684	as the module selects a default that is suitable for low to
685	moderate load.
686
687	IO::AIO::max_parallel $nthreads
688	Sets the maximum number of AIO threads to $nthreads. If more
689	than the specified number of threads are currently running, this
690	function kills them. This function blocks until the limit is
691	reached.
692
693	While $nthreads are zero, aio requests get queued but not
694	executed until the number of threads has been increased again.
695
696	This module automatically runs "max_parallel 0" at program end,
697	to ensure that all threads are killed and that there are no
698	outstanding requests.
699
700	Under normal circumstances you don't need to call this function.	879	Under normal circumstances you don't need to call this function.
701		880
		881	IO::AIO::max_idle $nthreads
		882	Limit the number of threads (default: 4) that are allowed to idle
		883	(i.e., threads that did not get a request to process within 10
		884	seconds). That means if a thread becomes idle while $nthreads other
		885	threads are also idle, it will free its resources and exit.
		886
		887	This is useful when you allow a large number of threads (e.g. 100 or
		888	1000) to allow for extremely high load situations, but want to free
		889	resources under normal circumstances (1000 threads can easily
		890	consume 30MB of RAM).
		891
		892	The default is probably ok in most situations, especially if thread
		893	creation is fast. If thread creation is very slow on your system you
		894	might want to use larger values.
		895
702	$oldmaxreqs = IO::AIO::max_outstanding $maxreqs	896	IO::AIO::max_outstanding $maxreqs
703	This is a very bad function to use in interactive programs	897	This is a very bad function to use in interactive programs because
704	because it blocks, and a bad way to reduce concurrency because	898	it blocks, and a bad way to reduce concurrency because it is
705	it is inexact: Better use an "aio_group" together with a feed	899	inexact: Better use an "aio_group" together with a feed callback.
706	callback.
707		900
708	Sets the maximum number of outstanding requests to $nreqs. If	901	Sets the maximum number of outstanding requests to $nreqs. If you do
709	you to queue up more than this number of requests, the next call	902	queue up more than this number of requests, the next call to the
710	to the "poll_cb" (and "poll_some" and other functions calling	903	"poll_cb" (and "poll_some" and other functions calling "poll_cb")
711	"poll_cb") function will block until the limit is no longer	904	function will block until the limit is no longer exceeded.
712	exceeded.
713		905
714	The default value is very large, so there is no practical limit	906	The default value is very large, so there is no practical limit on
715	on the number of outstanding requests.	907	the number of outstanding requests.
716		908
717	You can still queue as many requests as you want. Therefore,	909	You can still queue as many requests as you want. Therefore,
718	"max_oustsanding" is mainly useful in simple scripts (with low	910	"max_outstanding" is mainly useful in simple scripts (with low
719	values) or as a stop gap to shield against fatal memory overflow	911	values) or as a stop gap to shield against fatal memory overflow
720	(with large values).	912	(with large values).
		913
		914	STATISTICAL INFORMATION
		915	IO::AIO::nreqs
		916	Returns the number of requests currently in the ready, execute or
		917	pending states (i.e. for which their callback has not been invoked
		918	yet).
		919
		920	Example: wait till there are no outstanding requests anymore:
		921
		922	IO::AIO::poll_wait, IO::AIO::poll_cb
		923	while IO::AIO::nreqs;
		924
		925	IO::AIO::nready
		926	Returns the number of requests currently in the ready state (not yet
		927	executed).
		928
		929	IO::AIO::npending
		930	Returns the number of requests currently in the pending state
		931	(executed, but not yet processed by poll_cb).
721		932
722	FORK BEHAVIOUR	933	FORK BEHAVIOUR
723	This module should do "the right thing" when the process using it	934	This module should do "the right thing" when the process using it forks:
724	forks:
725		935
726	Before the fork, IO::AIO enters a quiescent state where no requests	936	Before the fork, IO::AIO enters a quiescent state where no requests can
727	can be added in other threads and no results will be processed.	937	be added in other threads and no results will be processed. After the
728	After the fork the parent simply leaves the quiescent state and	938	fork the parent simply leaves the quiescent state and continues
729	continues request/result processing, while the child frees the	939	request/result processing, while the child frees the request/result
730	request/result queue (so that the requests started before the fork	940	queue (so that the requests started before the fork will only be handled
731	will only be handled in the parent). Threads will be started on	941	in the parent). Threads will be started on demand until the limit set in
732	demand until the limit set in the parent process has been reached	942	the parent process has been reached again.
733	again.
734		943
735	In short: the parent will, after a short pause, continue as if fork	944	In short: the parent will, after a short pause, continue as if fork had
736	had not been called, while the child will act as if IO::AIO has not	945	not been called, while the child will act as if IO::AIO has not been
737	been used yet.	946	used yet.
738		947
739	MEMORY USAGE	948	MEMORY USAGE
740	Per-request usage:	949	Per-request usage:
741		950
742	Each aio request uses - depending on your architecture - around	951	Each aio request uses - depending on your architecture - around 100-200
743	100-200 bytes of memory. In addition, stat requests need a stat	952	bytes of memory. In addition, stat requests need a stat buffer (possibly
744	buffer (possibly a few hundred bytes), readdir requires a result	953	a few hundred bytes), readdir requires a result buffer and so on. Perl
745	buffer and so on. Perl scalars and other data passed into aio	954	scalars and other data passed into aio requests will also be locked and
746	requests will also be locked and will consume memory till the	955	will consume memory till the request has entered the done state.
747	request has entered the done state.
748		956
749	This is now awfully much, so queuing lots of requests is not usually	957	This is not awfully much, so queuing lots of requests is not usually a
750	a problem.	958	problem.
751		959
752	Per-thread usage:	960	Per-thread usage:
753		961
754	In the execution phase, some aio requests require more memory for	962	In the execution phase, some aio requests require more memory for
755	temporary buffers, and each thread requires a stack and other data	963	temporary buffers, and each thread requires a stack and other data
756	structures (usually around 16k-128k, depending on the OS).	964	structures (usually around 16k-128k, depending on the OS).
757		965
758	KNOWN BUGS	966	KNOWN BUGS
759	Known bugs will be fixed in the next release.	967	Known bugs will be fixed in the next release.
760		968
761	SEE ALSO	969	SEE ALSO
762	Coro::AIO.	970	AnyEvent::AIO for easy integration into event loops, Coro::AIO for a
		971	more natural syntax.
763		972
764	AUTHOR	973	AUTHOR
765	Marc Lehmann <schmorp@schmorp.de>	974	Marc Lehmann <schmorp@schmorp.de>
766	http://home.schmorp.de/	975	http://home.schmorp.de/
767		976

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines